1. Field of the Invention
The present invention relates to a semiconductor device having a circuit composed of a thin film transistor (hereafter referred to as TFT), and to a method of manufacturing thereof. For example, the present invention relates to an electro-optical device, typically a liquid crystal display panel, and to electronic equipment loaded with that kind of electro-optical device as a part.
Note that, throughout this specification, the term semiconductor device specifies devices in general which function by utilizing semiconductor characteristics, and that electro-optical devices, semiconductor circuits, and electronic equipment are all semiconductor devices.
2. Description of the Related Art
Techniques of forming thin film transistors (TFTs) using a semiconductor thin film (with a thickness on the order of several tens to several hundreds of nanometers) formed on a substrate having an insulating surface have been in the spotlight in recent years. Thin film transistors are widely applied in electronic devices such as an IC or an electro-optical device, and in particular, their development as a switching element of a pixel display device has been accelerating.
For example, a liquid crystal display device is a device in which a TFT is placed in each of several million pixels laid out in a matrix shape, and by controlling the electric charge applied to each pixel electrode by the switching function of the TFTs, the electro-optical characteristics of a liquid crystal is changed, and image display is performed by controlling the light transmitted through a liquid crystal panel.
An IPS method (recorded in Japanese Patent Application Laid-open No. Hei 6-160878) of controlling an electric field in the horizontal direction, with respect to a substrate, in a parallel electrode structure, is known as a method of driving this type of liquid crystal display device.
A liquid crystal display device driven by this IPS method can be driven at a low voltage, and compared to other driving methods (such as a TN method or a STN method), the IPS method has a characteristic of a larger viewing angle.
Further, an IPS liquid crystal display device has a TFT, a gate line, a source line, a pixel electrode, a common line, and a common electrode, extending from the common line in a pixel region, on the same substrate. In order that the electric field applied to a pixel electrode does not impart any influence on another pixel, each pixel electrode is structured as sandwiched by the common electrode arranged in parallel to the pixel electrode. The electrode surface area necessary for these electrodes therefore reduces the aperture ratio of the IPS liquid crystal display device.
Furthermore, in order to ensure the electric charge retention time in a general liquid crystal display device, it is necessary to form a storage capacitor. A sufficient electrode surface area is necessary in order to form a storage capacitor also in the IPS liquid crystal display device, and therefore the aperture ratio is reduced.
In addition, if the wirings and the electrodes are made minuter in order to increase the aperture ratio, then it becomes difficult to ensure a sufficient storage capacitance.
An object of the present invention disclosed in this specification is to provide a technique for solving the conventional problems stated above. Namely, an object of the present invention is to provide a proposal of a method of forming a storage capacitor in an IPS liquid crystal display device, and to provide a technique of forming a pixel region having a high aperture ratio.
A structure of the present invention disclosed in this specification is a semiconductor device having a pair of substrates and a liquid crystal layer sandwiched by the pair of substrates, characterized in that:
a pixel electrode is formed on one substrate out of the pair of substrates;
an electric field parallel to the face of the substrates is applied between the pixel electrode and a common electrode; and
a capacitor is formed by the common electrode, an anodic oxide film of at least a portion of the common electrode, and the pixel electrode formed on the anodic oxide film.
Further, the above structure is characterized in that the common electrode is made from a material which can be anodically oxidized.
Another structure of the present invention is a semiconductor device having a pair of substrates and a liquid crystal layer sandwiched by the pair of substrates, characterized in that:
a pixel electrode is formed on one substrate out of the pair of substrates:
an electric field parallel to the face of the substrates is applied between the pixel electrode and a common electrode;
a capacitor is formed by the common electrode, an anodic oxide film of at least a portion of the common electrode, and the pixel electrode formed on the anodic oxide film; and
the liquid crystal layer is surrounded by a sealing material, and spacers are formed in the region in which the sealing material is formed.
Further, another structure of the present invention is a semiconductor device having a pair of substrates and a liquid crystal layer sandwiched by the pair of substrates, characterized in that:
a pixel electrode is formed on one substrate out of the pair of substrates;
an electric field parallel to the face of the substrates is applied between the pixel electrode and a common electrode;
a capacitor is formed by the common electrode, an oxide film of at least a portion of the common electrode, and the pixel electrode formed on the oxide film;
a spacer is formed in a region between a pixel portion, in which the pixel electrode is formed, and a driver circuit; and
a spacer is formed in a region in which an element of the driver circuit does not exist.
Further, another structure of the present invention is a semiconductor device having a pair of substrates and a liquid crystal layer sandwiched by the pair of substrates, characterized in that:
a pixel electrode is formed on one substrate out of the pair of substrates;
an electric field parallel to the face of the substrates is applied between the pixel electrode and a common electrode;
a capacitor is formed by the common electrode, an anodic oxide film of at least a portion of the common electrode, and the pixel electrode formed on the anodic oxide film; and
a spacer exists on a contact portion of the pixel electrode.
Furthermore, the above structures are characterized in that the oxide film is formed through an anodic oxidation process in which the applied voltage/voltage supply time ratio is equal to or greater than 11 V/min.
In order to realize the above structures, a structure of the present invention is a method of manufacturing a semiconductor device, having the steps of:
forming a resin film on a TFT;
forming a common electrode on the resin film;
forming an oxide film of the common electrode; and
forming a pixel electrode covering at least a portion of the oxide film,
wherein a capacitor is formed by the common electrode, the oxide film of the common electrode, and the pixel electrode.
Further, another structure of the present invention is a method of manufacturing a semiconductor device, having the steps of:
forming a resin film on an upper part of a TFT;
forming an inorganic film on the resin film;
forming a common electrode on the resin film;
forming an oxide film of the common electrode; and forming a pixel electrode covering at least a portion of the oxide film,
wherein a capacitor is formed by the common electrode, the oxide film of the common electrode, and the pixel electrode.
In addition, the above structures are characterized in that sputtering is used for the step of forming the inorganic film on the resin film.
Furthermore, the above structures are characterized in that the step of forming the oxide film is an anodic oxidation process in which the applied voltage/voltage supply time ratio is equal to or greater than 11 V/min.